Fanum
Toubab
Place the heated grips on a length of stiff foam 'or similar' wire them to the bike with an in-line jack plug (this gives any easy break point if the passenger leaves the bike without un-plugging).
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Certainly an inline plug needed, but not a Jack type (if you mean the sort I'm thinking of, like a stereo jack?)
Those would pop a fuse every time they're connected/disconnected.
A powerlet plug might be the answer....and they're adaptable for all sorts of other things once it's fitted to the bike